The invention relates to a method for the diagnosis of natural vibrations in a mechatronic system, for example a machine tool, packaging machine and other manufacturing machines, e.g. in the form of a robot. These mechatronic systems normally include a plaurality of machine elements, including drives, which cause unwanted vibrations during operation of the system. Each one of these vibrations results from a combination of forced vibrations, caused by external forces or unbalances for example, as well as from natural vibrations which are encountered when one or more of the resonances of the machine are excited. These vibrations adversely affect the quality of products produced by the mechatronic system, so that ways to substantially reduce these vibrations are searched for.
Computation and visualization of these vibrations therefore gain increasingly importance. This is true in particular for the area of vibration diagnosis. This refers hereby essentially to the effect which the machine elements of the mentioned complex mechatronic systems have on the dynamic behavior of the overall system.
The purpose of vibration diagnosis is to make the technical designer of a mechatronic system understand as clearly as possible the vibration behavior of the system in order to give him a tool to use constructive measures and/or select materials for inhibiting vibration.
For diagnosis of natural vibrations of a mechatronic system, it is necessary to excite it. Conventional methods use external vibration exciters, so-called translatory shakers, which are attached at different points of a rigid body of a mechatronic system. Vibrations of different frequencies are impressed upon the rigid body via these shakers. At different areas of the rigid body, especially at its corner points, sensors, for example by means of displacement measuring systems, accelerometers, pressure gauges, etc., are used to detect the natural vibrations.
A mathematical model of the vibration behavior of the overall system can be formed on the basis of the measured values. As all system components are, however, interconnected, a system of coupled differential equations is obtained which are converted by means of model analysis, i.e. by means of an algorithmic mathematical uncoupling, into different scalar equations, so that information can be provided about the natural frequency, the attenuation, and form of the vibration for each mode of a natural vibration.
On the basis of these equations, a model of the mechatronic system can be simulated and visualized by means of a simple wire-frame model for example. Such wire-frame models are conventional and are constituted by corner points where sensors are typically attached in such a manner that a maximum yield of information is obtainer. The design engineer thus is given insight into the system dynamics and can take vibration-absorbing constructive measures through modification of the oscillation parameters that are now known.
The process set forth above for generating natural vibrations using shakers external to the system has the drawback that the drives and their part components are not included in the vibration diagnosis and the simulation.
Conventional software packets for model analysis identify and represent vibration modes in such a manner that either translatory or rotatory degrees of freedom are related to. A simultaneous visualization of both types of degrees of freedom is achieved in practice by so including the rotatory degrees of freedom into the holistic visualization that rotatory vibration modes are stimulated using movements of a rigid body in relation to a fixed point. However, this approach does naturally not take into account the compliance that continuously exists between mechanical structure and drives.